Exemplary embodiments of the invention relate to a device for opening or closing a seal seat of a valve, which is provided for arrangement in a pipe for liquid or gaseous media.
Valves are used, for example, where a pipe for liquid or gaseous media is to be opened or closed. In the closed condition of the valve, a very limited leakage rate must be ensured by the valve. Depending upon the application the valves can be provided for multiple or also only for single actuation, the latter being the case for example in drive systems for space travel applications.
In technical systems a distinction is made between Normally Open (NO) and Normally Closed (NC). The designation elates to the switching state before actuation. For example a NO valve is closed upon actuation.
In the case of space travel applications high standards are set for the reliability of the activation, since a malfunction can cause substantial damage or even the loss of the drive system.
Exemplary embodiments of the present invention are directed to a structurally and/or functionally reliable device for opening or closing a fluid line as well as a corresponding drive system for space travel applications.
In a device for opening or closing a seal seat of a valve that is provided for arrangement in a pipe for liquid or gaseous media, according to the invention a shape memory actuator is provided for once-only activation of the valve, the memory actuator changes its external shape abruptly when a transformation temperature is reached which is dependent upon its alloy composition. The transformation temperature can be generated by a controllable electrical heating device of the device.
The use of a shape memory actuator enables the once-only and irreversible activation of the valve. The activation takes place by heating the shape memory actuator using the energy supplied from the exterior, i.e. the heating device, so that the actuator changes in size abruptly and as thereby irreversibly changes the current open or closed state of the valve. This operating function can be provided with great reliability. For operation of the valve no further elements are necessary in addition to the shape memory actuator and the heating device, so that the device has a simple mechanical structure. The device can be produced with few components. The device can be provided with a low weight.
The valve may comprise a piston disposed in a distribution compartment and which, depending upon whether the valve is opened (NO) or closed (NC) without activation of the shape memory actuator, is or is not pressed by a spring against the seal seat, wherein the shape memory actuator generates a force directed counter to the spring on the piston.
The piston can be released from the seal seat or pressed onto the seal seat by the activation of the shape memory actuator depending upon whether the valve is opened or closed without activation of the shape memory actuator. Thus, the piston is moved by the actuation of the shape memory actuator. For this purpose when the transformation temperature is reached the shape memory actuator generates a force which is greater than the force generated by the spring in order to move the piston.
The force of the shape memory actuator, i.e. the force applied by the shape memory actuator to the piston, corresponds in the non-activated state to the force generated by the spring. In other words, there is a balance of forces, so that the valve—according to the constructive configuration—is either in the condition NO (normally open) or NC (normally closed). In the non-activated state the shape memory actuator has its so-called “cold” structural state.
The movement of the piston is only dependent upon the balance of forces of the spring and the shape memory actuator. This can be achieved, for example, by the spring and the shape memory actuator, lying for example in a common axis, being disposed on opposing sides of the piston.
The shape memory actuator may have a spiral shape and the heating device may be disposed in the interior of the spiral shape memory actuator. This enables fast heating of the material of the shape memory actuator in the event of the heating device is activated. A uniform heating of the material of the shape memory alloy is achieved until the transformation temperature is reached. For reasons of redundancy the heating device can also be implemented by a plurality of heating elements.
The distribution compartment can be coupled to at least two connections, so that the liquid or gaseous medium can flow through a connection into the distribution compartment and the liquid or gaseous medium can flow through another connection out of the distribution compartment if the valve is opened.
The seal seat can be formed by a metal seal, which in the sealed state is pressed against a counterpart. The metal seal can be formed in particular from a ductile material that is plastically deformable when pressed against the counterpart. In this way a low leakage rate can be ensured before actuation for a NC (normally closed) valve or after actuation for a NO (normally open) valve.
The heating device can comprise a safety device that deactivates the heating device after the transformation temperature of the shape memory actuator is exceeded. As a result after the operation of the valve damage by the heating device due to excessively high temperatures can be prevented. The switching off of the heating device is also ensured when an activation for a switching element or the switching element for the heating circuit itself are defective.
The valve is constructed so that it is rotationally symmetrical with respect to the components that are necessary for the sealing function. This results in a simple and space-saving construction of the device.
The valve can comprise three connections and two seal seats, wherein one of the connections is closed by a dummy cap. As a result, depending upon which connection is closed by the dummy cap, a NO (normally open) or NC (normally closed) function can be implemented as required. Such a device can be used flexibly, since at the time of production it is not yet necessary to fix the function (NO or NC).
To summarize, in the present invention a valve is activated with a one-way effect shape memory actuator. The shape memory actuator in a suitable configuration changes its external shape abruptly when a transformation temperature dependent upon the alloy composition is reached. The strong forces released in this case are used for the opening and closing of a metal seal seat. The transformation temperature is reached by means of an electrical heating device. The valve can be designed to be actuated once precisely, and in its field of use it is similar to a pyrotechnic valve.
Furthermore a drive system for a space travel application is proposed, which has at least one device of the type described above. The drive system has the same advantages as those mentioned in connection with the device described above.